Temperature control system



June 16, 1942. w. L. MGRATH. 7 2,286,296

TEMPERATURE CONTROL SYSTEM v I Filed Dec. 24, 1958 a Sheets-Sheet 1 June.16, 1942.

W. L. M GRATH TEMPERATURE CONTROL SYSTEM Filed Dec. 24, 1938 3Sheets-Sheet 2 ihmmtot mmmmm.msaa

Patented June 1 1942 o 1 UNITED. STATES PATENT rnmrsm'runa common srsrmWilliam L. McGrath, St. Paul, Minn, asslgnpr to Minneapolis-HoneywellRegulator Company, Minneapolis, Minn, a corporation of Delawareapplication December 24, 1933, Serial No. 241,565

(or. zoo-es) 16 Claims This invention relates to temperature control,being directed more particularly to an gimproved means for determiningthe load upon temperature changing equipment and for varying thetemperature changing effect of the equipment in accordance with theload. While-the following explanation and description for pur turecontrol, my invention may be used in controlling other conditions orforces similarly.

More specifically, my invention deals with a device responsive to theratio between the on time and oh time of a thermostat which causesintermittent operation of temperature changing equipment for maintaininga giventemperature. My present invention relates in some respects to myprior inventions disclosed in Patents Numbers poses of clearness willdeal mainly with tempera- 7 temperature changing efiect of a temperaturechanging means is intermittently increased and decreased and thetemperature changing eilect is automatically varied in accordance withthe relationship between the time that the temperature changing means isoperating at an increased rate and the time that it is operating at adecreased rate.

Another object is the provision of a device for measuring the load onintermittently. operated temperature changing equipment which will takea substantially predetermined position in re sponse to the relationshipbetween the time the equipment has been operating and the time it hasnot been operating.

Another object is the provision of a valve controlled by a heat actuateddevice which is heated when a controlling thermostat is on andvisnotheated when the thermostat is ofi, the device asan improved deviceresponsive to the aggregate duration of on cycles relative to theaggregate duration of off cycles of operation for varying thetemperature changing rate.

suming a position proportional to the relation between aggregate on andoff time of the thermostat.

Another object is the provision of a stage heating system having adevice operable to control at least one stage of heating depending onthe ratio of "on" time to on time of operation during a given incrementof time.

Another object is the provision of a thermostatically controlled heatingsystem having a device in the form of a heat actuated switch which coolswhen the thermostat is satisfied and heats Another object is theprovision of a device responsive to the relationship between theduration of on cycles'and oiicycles of the thermostat, the device takingthe form of a heat actuated switch so arranged that. the switch willassume a substantially predetermined position depending upon the rate ofheat input to the switch, the rate of heat input being determined by therelative amount of heating of the switch interms of the when thethermostat is calling for heat and which may operate to vary heatingdepending upon the relative heating and cooling of the switch as timegoes on. I

Another object is the provision in a stage heating system of a heatactuated switch having substantial thermal mass, heating of the switchbetime that the thermostat is indicating a need for operation of thetemperature chan ing equipment.

Another object isthe provision of improved means for automaticallyadjusting a temperature changing device in accordance with the loaddemands in an on" and ofi temperature control system without the use ofoutdoorv thermostats and without permitting the indoor temperature todeviate more than a slight increment from a predetermined value wherebymore efllcient cycling and improved control is obtained.

Another object is the provision of improved means for controllingtemperature wherein the fired two-stage heating system employing my in-I ing controlled primarily by a thermostat and the heating means havingdifferent characteristics when the switch is closed, the switchcontrolling at least one stage of heating.

The exact nature of my invention and its manifold advantages will becomeapparent from the accompanying detailed description and drawings ofrepresentative embodiments thereof; it being understood that mydisclosure of temperature' control systems is illustrative of otherarrangements inwhich .the principles of my invention may be employed. 7

Figure 1 is a diagrammatic showing ota vention wherein two burners areprovided.

Figure 2 is a diagrammatic showing of a heat- OFFICE vention.

Figure 4 represents a further form. of my invention.

Referring to Figure 1 of the drawings, numeral designates generally awarm air furnace having a combustion chamber 2 which is enclosed by ajacket 3, the upper part of which forms a bonnetfor the furnace.Disposed within the combustion chamber 2 are gas burners 4 and 5 whichmay be of a conventional type, the burner 5 being supplied with fuelthrough a conduit 6 which may connect to a gas supply main. The burner 4is supplied with fuel through a branch conduit 1 connected to theconduit 6. Interposed in the conduit 6 ahead of the branch connection 1is an electric control valve 8 and in the conduit 6 beyond the branchconnection 1 is a hand valve 9. Interposed in the branch conduit 1 is anelectric fuel control valve Ill similar to the valve 8 and ahead of thisvalve in the conduit 1' is a hand 44 cooperating with fixed electricalcontacts 45 and 46, the said contacts being engaged by their respectiveswitch blades when the relay is ener- As will become apparent from thedescription of operation following,'the burner 4 provides for a secondstage of heating and is controlled by a switch device 48. The device 48comprises a metal block 49 having substantial thermal mass within whichis positioned a bimetal element 50 which cooperates with afixedelectrical contact 5|. A permanent magnet 52 is provided for im-'parting snap opening and closing movements to the switch formed by theelement 50 and contact 5|. An electrical heating resistance 53 isarranged adjacent the block 49 and an electrical circuit through theheating resistance may be formed through either of two variableresistances 54 and '55 or through both of them, that is, parallelcircuits maybe formed through the variable resistances both extendingthrough the heating resistance 53. The variable resistances 54 and 55-includes manually slidable contacts valve corresponding to the valve 3.Arranged adjacent the lower burner 5 is a small pilot burner |5 which iscontinuously supplied with fuel through a tube It communicating with theconduit'S ahead of the valve 8. Numeral i1 desi nates a safety pilotwhich may be of conventional type comprising a bimetal element It!adjacent the flame of the pilot\burner and which is normally flexed intoengagement with a fixed electrical contact I 3 when the pilot burner isburning.

An exhaust fan 2| which takes suction from the interior of thecombustion chamber through a suction duct 22 is provided for producing aforced circulation of draft through the combustion chamber. Fan 2|discharges through a duct 23 and is driven by an'electric motor having aterminal box indicated at-24. In the discharge duct 23 of the fan 2| isthe operating element of a sail switch 25, the purpose of which will bepresently described. The switch 25 comprises a pivoted lever element 26,the lower end of which is weighted and which is' movable in response tothe exhaust through the duct 23 and the upper end of which carries amercury switch 21. Whenever the exhaust fan 2| is operating, the leveras the one shown at to deliver air to individual rooms. Air from all thespaces being heated may be returned to the furnace through a commonreturn duct 3| communicating with the lower part of the furnace Jacket.

My system is-automatically controlled and it is rimarily under thecontrol of a space thermostat 32 which may be of a known type comprisinga bimetal element 33 operable to move a pair of resilient switch blades34 and 35, the blade 34 cooperating with a fixed electrical contact 36and the blade cooperating with a fixed elec- 58 and 51, respectively.

With the parts of the apparatus in the position shown. on the drawing,the thermostat is satisfied and the heating equipment is not inoperation; The thermostat 32 is of the type such that the blade 35engagesits associated contact at a predetermined temperature and theblade 34 engages its associated contact at a predetermined energizingcoil 42 will be completed as follows:

from fixed contact through a wire 50, wire 6|, coil 42, wire 62,secondary winding 43 of transformer 33, wire 63, fixed contact 31, andblades 35 and 34 of thermostat 32. Immediately upon completion of thiscircuit, coil 42 will be energized and switch blades 43 and 44 will bemoved into engagement with their associated contacts. As soon as switch43 closes'a maintaining circuit for coil 42 will be completed asfollows: from fixed contact 3101' thermostat 32, throughwire v 53,secondary winding 40, wire 62, coil 42, wire 6|, wire 64, switch blade43, fixed contact 45, wire 55, and through the thermostat 32 back tofixed contact 31. It will be seen thatthis circuit is independent ofthermostat blade 36 and fixed contact 36 so that once the coil 42 hasbecome energized it will remain energized through the maintainingcircuit until the temperature has again risen above 70, the temperatureat which blade 35 engaged fixed contact 31. Thus the thermostat has adefinite operating differential and chattering of the relay due tovibration of the thermostatic contacts is eliminated.

trical contact 31. Low voltage power is supplied I from a transformer ofthe voltage step-down type indicated at 33 and comprising a primarywinding 33 and a secondary winding 40, the primary winding having agreater number of turns than the secondary winding. Numeral 4| indicatesa relay comprising a 'relay winding 42 arranged to actuate a pair ofswitch blades 43 and Also upon energization of relay coil 42 and closureof switch 44, a circuit'energizing the motor driving fan 2| is completedas follows: from a line conductor 10 to contact 46, switch blade 44,wire 56, wire 51, motor terminal box 24, and wire 68 connecting to lineconductor 63, the line conductors-is and 10 being connected to a'sourceof external power, not shown. Operation of the fan 2| will scavenge theinterior of the combustion chamber and as soon as draft has beenestablished through the discharge duct 23, the mercury switch 21 will bemoved to closed position and a circuit for energizing and opening thecalling for heat.

- continue as long as the thermostat is calling for heat. At the sametime that the circuit for opening valve 8 is completed and heatingstarted, a circuit for energizing the electrical heating resistance 53is completed as follows: from line conductor 10 to fixed contact 6,switch blade 44, wire 66, wire ll, wire 77, resistance 53,'wire 78, wire19, a part of resistance 54, contact 56,

wire 80 and wire i3, wire 14, safety pilot l1, wire.

15, mercury switch 21' back to line conduc or 59. Heat from resistance53 will tend to heat the metal block 49 as long as thermostat 32 isWhenever the thermosat 32 becomes satisfied, it will causedeenergization of the above described circuits so as to terminateheating. When thermostat 32 again calls for heat the above describedcircuits will again be completed and heating will again commence in themanner described. Heater 53 will again be energized and heat will againbe applied to the metal block 49. In this manner as the thermostat 32cycles on and 03, the device 63 will be heated at intervals, heat beingdissipated between times when the device is not being heated.

The thermal switch is arranged to have such mass that its response to asingle heating cycle is unsubstan ial but its position will correspondto a rateof heat input to the device determined by the aggregate amountof time that the thermos at has been demanding heat over a substantialperiod of time. The rate of heat input to the device 8 determined by theaggregate amount of time that the thermostat is calling for heat will beequivalent to a steadysustained rate of heat input at which the device48 would accumulafe heat until a certain temperature were reached atwhich the dissipation of heat from the device would be such that thetemperature would level oil and remainat a certain value. Element 50would, of course, assume a position corresponding to this temperaturevalue. It will be seen therefore that for a fixed heating lead and acorresponding fixed rate of heat input to the device 48, the element 50will not continuously progress in one direction or the other but assumea substantial predetermined position. corresponding to the heating load.As the heating load on the building increases, the duration of on.cycles relative to oil cycles of the thermostat 32 will increase and therate of heat input to block 49 will correspondingly increase, element 50assuming a position closer to the contact 5|. As will now be obviouswhen the heating load has increased to a certain value, the aggregateduration of on cycles with respect to oil cycles will have increasedsufiiciently to cause assessesv for is. Upon completion of this circuitthevalve II is opened and fuel is supplied to the burner l whereby asecond stage of heating commences. Increasing of the heating capacity ofthe furnace in this manner in accordance with the load will enable theapparatus to more readily heat the the temperature at the building andmaintain desired value. i From the foregoing, it should be understoodthat the device 48 in bringing on the-second stage .of heating hasmeasured the-heating load very accurately inasmuch as the device unlikean outdoor thermostat, takes into 'consideration all factors whichcontribute to the heating loadll After a sustained increased load hasonce brought on the second stage of heating the increased heating ratewill tend-to shorten the on cycles of the thermostat. This would causethe system .to return to first stage operation unless compensated for.Therefore I provide an ar rangement for varying the characteristics ofthe heating element 53 so that once the second stage comes on it willstay on in the absence of a load 1 resistance 55, contact 51', wire 85,wire 82, contact 5!, element 50, wire 83, wire i4, safety pilot ll, wireit, mercury switch 21, wire 16 back to line conductor 69. Because ofthis additional parallel circuit through the heater'53 the amount ofcurrent passing therethrough be increased and the amount of heating willcorrespondingly be increased. The additional heating will tend to morefirmly flex the element into engagement with the contact 5|. Theincreased heating at-element 53 will compensate for the shorter oncycles of the thermostat so that the rate of heat input to the device 48is notdecreased when the system goes on second stage operation. Uponsubsequent cycles of the thermostat both stages of the heatingsysfemwill be brought on simultaneously and this second stage operation willcontinue as the thermostat '32 cycles until there is an appreciable dropin the heaing load causing the duration of the on cycles to becomeshorter with respect to the off cycles to such an extent that there willbe sumcient cooling of theblock 49 drawing ofi' cycles to cause theelement 50 to flex away from the contact 5!.

From the foregoing the manner of operation of my system embodying theparticular device which I'have describedshouldbe clearly understood bythose skilled in the art. The unusualprinciple iipon which it operatesoffers new-advantages in the field of temperature control whereby moredesirable and satisfactory results can be secured with extremely simpleand inexpensive apparatus. Devices heretofore employed for sensing theheating load for purposes of dethe element 50 to'move into engagementwith the contact 5|. When'this occurs, anelectric circuit will becompleted for energizing thevalve ID as follows: from line conductor 10through fixed coritact 46, switch hlade ll, wire 66, wire ll, wire 88,valve), wire 8|, wire 82, fixed contact 5|, element 50', wire 83, wirell, safety pilot l1, wire I5, mercury switch 21 back tolineconductermining what amount of heating is necessary have been responsiveto temperatures and such devices are always subject to numerous errorproducing factors" such as variation in the rate of heat leakage of abuilding, the number of doors and windows open;v etc. My inventionobviates the necessity of ftwo-stage thermostats and the like and ismore eflicient than'known types of devices of asimilar nature inasmuchas the indoor temperature need not deviate from a predetermined valuefor bringing on a second stage operation.

In the past bonnet temperature responsive devices have been; used toinitiate second stage .In Figure 2 I have shown a second modification ofmy invention wherein I have applied the invention to the control of amulti-speed furnace fan rather than to the control of a plurality ofburners. Those elements of Figure 2 which are identical withcorresponding elements of Figure 1 are numbered the sameand otherelements are numbered with numbers greater than 100. The furnace I ofFigure2 is similar to that of Figure .1 but fuel is supplied by means ofa motordriven fuel burner IOI, the motor of which has a terminal boxI02. In the system of Figure 2, air is forcibly circulated to the spacesbeing heated by means of a furnace fan I03 which draws air from thespaces being heated and forces it through the furnace jacket where it isheated and thence through the distributing conduit 29' coil winding I08arranged to actuate a switch blade I09 cooperating with a fixedelectrical contact IIO the switch being closed when the relay isenergized. The relay 101 comprises a coil winding III arranged toactuate a switch blade II2 which cooperates with fixed electricalcontacts H3 and H4, blade II2 engaging contact II4 when coil III isdeenergized and contact II3 when coil.IlI is energized.

Responsive to the temperature within the furnace bonnet is a switchingdevice generally indicated at I", this device comprising two mercuryswitches I I8 and H9 both of which are arranged thereto for vary n theamount of resistance in circuit with the contact. As in the previouslydescribed embodiment of the invention, an electrical circuit may beformed through the heatingresistance I53 and the resistance I55. Onlyone variable resistance is used in the present modification for reasonswhich will presently be seen.

In the present embodiment of the invention,

the thermostat 32 controls the relay 4I in exactly the same manner asdescribed in the previous embodiment and therefore this description ofoperation need not be repeated. Whenever relay 4! is energized, switchblade. 44 engages contact 46 completing a circuit for energizing thefuel burner motor as follows: from line conductor I0 to a wire I22, wireI23, contact 46, switch blade 44, wire I24, wire I25, mercury switchII8, wire I26, motor terminal box I02, and wire I21 back to lineconductor 69. As soon as the circuit just described is completed, thefuel burner I III is started in operation for supplying fuel to thecombustion chamber to begin heating, it being understood that the systemincludes conventional mechanism for igniting the fuel from lineconductor I0 through wire I22,wire

I23, contact 46, blade 44, wire I24, wire I28, wire I29, heater I53,wire I30, wire I3I, part of resistance I55, contact I51, wire I32, wireI33,

.mercury switch II9, wire I34 back toline conductor 69. As soon as thiscircuit just described is completed, heater element I53 will begin tosupply heat to the device I48. The circuit for energizing relay I06 isas follows: from line conductor 10 through wire I22, wire I23, wire I58,

' wire I36, winding I08, wire I31, wire I38, wire to be actuated by ahelical bimetal thermostatic element I20 disposed within the furnacebonnet.

Upon the air in the bonnet being heated to a predetermined temperature,the switch I I9 will be moved to a closed position. The switch H8 isnormally closed and is only open upon the occurrence of a predeterminedhigh temperature in the bonnet, this switch being a high limit switch aswill presently become apparent.

The device in Figure 2 which controls the second stage operation of thesystem is very similar to that of Figure 1 but is slightly modified inthat instead of using a metal block having substantial thermal mass thebimetal switch is enclosed within an insulating housing in order toretard the dissipation of heat from the heating element.

" Referring to the device I48, it comprises a flexible 'tact withcontact II4.

I33, mercury switch II9, andwire I34 back to line conductor 69. As soonas the circuit just described is completed energizing relay I06, switchblade I09 will be moved into engagement with contact IIO completing'acircuit for energizing the motor I04 for operating the fan I03 at itsfirst stage speed, it being understood that the switch blade II2 remainsat present in con- The circuit now completed for the fan motor is asfollows: from line conductor 10, through wire I22, wire I39, contact II0, switch blade I09, wire I40, switch blade II2, contact II4, wire I4I,a terminal I42 of terminal box I 05 through the appropriate motorwindings. terminal I43 and wire I44 back to line conductor 69. Warm airwill now be forcibly circulated to the spaces being heated, the fanoperating asheat was. supplied by the element I53 substantially during,the tim e thatheatin .Was in progress. During the time that thethermostat is satisfied, the device I48 will cool as in the previousembodiment. a

. nace at a fasterrate so that the bonnet temperature and thetemperature of the circulating air will be lower; This will-not tend toshorten the thermostatic cycles so the additional circuit for elementI53 is not necessary. While the heating load remains substantially the:same now or increases the thermostat will cycle on and off, the systemoperating at its second or increased stage air. supply .rate during eachon rounding atmosphere. The thermostat 32 will now cycle onand off. theon and ofi intervals dependingupon the magnitude of the heating load. Asin the previous embodiment, the relative duration of on and of: cycleswill produce 1 relative heating and cooling of the device I48 which willamount to a heat input rate to the device equivalent to a certain steadycontinuous heat input to the device'at which the element I50 will assumea predetermined net position, that is, depending upon the rate of heatinput to the device I48 its temperature will eventually 'level 011 at acertain value at which, continued heat input at the same rate will nolonger cause the temperature to continue rising. The element I50 isdesigned to have suflicient mass so that its movement in one directionor the other upon heating or cooling during a single cycle is very smallbut that after a number of cycles depending upon their relativeduration, and therefore uponthe equivalentrate of heat input to thedevice I48, the element I50 will assume a cer tain net position at adistance from the contact I5I corresponding to the rate of heat input.When the heating load has increased until the ratio of 'the duration ofon cycles to oif cycles has reached a predetermined amount, element I50will make contact with i5I bringing on the second stage of fan operationin a manner similar to that described ,in the previous embodiment. Inall probability this will occur during an on cycle of the thermostatwhen heating is in progress and when element I50 does engage contact I5Ia circuit energizing the relay I01 is completed. The circuit referred toabove for energizing the relay I01 is as follows: from line conductor 10through wire I22, wire I23, wire I58, wire I63, winding III, wire I54,wire .I6I,-

of blade II2 with contact H3, a circuit is completed for energizing theappropriate windings of motor I04 for operating the motor atits sec- 0ndstage or relatively high speed. This'circuit is as follows: from lineconductor '10through wire I22, wire I39, contact H8, blade I08, wireI40, blade H2, contact 3', wire I64, terminal will now be operated at arelatively high speed forcibly circulating heated air to the spacesbeing heated at a greater rate. It will be seen therefore that when theheating load has increased to a certain amount as measured by the deviceI48, the rate oi supply or'heated air is 1 increased. Increased fanspeed will not cause a greater amount oi heat to be carried to the It isto be appreciated that the apparatus for.

- c 8 I83 of terminal box I05, through the appropriate windings of motorI04, terminal I43 and wire I44 back to line conductor 88. Thefan I83 aburner 204 by a conduit 201.

cycle of the thermostat, the element I50 remaining in engagement withthe contact I5I.

From the foregoing. it should be apparent that the embodiment of Figure2 of the invention has all the advantages and utilities enumerated abovein connection with the embodiment of Figure 1.

bringing about second stage operation is of a very reliable nature, yetembodying the utmost. simplicity. By merely manipulating the variableelectrical resistance which I have provided, the system may be adjustedto operate at second stage capacity at any desired heating load.Obviously, the device I48 and its adjustment means can be used with anythermostatically or correspondingly controlled apparatus inasmuch as thefunction of the device I48 is not in any way dependent upon the size ofthe. objective being treated or its particular characteristics.

Referring to the modification of Figure 3v of the drawings I have showna somewhat difiere'nt adaptation of my invention wherein the heatingcapacity of the system is gradually changed in accordance with the load.In Figure 3 numeral 2I0 designates a known type-of diaphragm gas controlvalve comprising a valve body 2 having an inlet 2I2 and an outlet 2I3.Passage of gas through the-valve is controlled by a valve member 2 I4movable by a flexible diaphragm H8 and cooperable with a seat 208. Theedges of I the diaphragm 2I6 are sealed between a periphrelation by abolt 222. and a disc nut 223. An

aperture 224 extends through the bolt 222 providing communication fromthe inlet side. of the a valve to the chamber above the diaphragm. Themanner of operation of the valve M0 is well known in the art, the valvebeing closed whenever there is pressure above .the diaphragm and thevalve being opened when the pressure above the diaphragm is released.

Fuel is supplied to the valve from a conduit 225. and the outlet of thevalve is connected to Adjacent the, burner 284 is a pilot burner 2I5which is continuously supplied with gas through-a tube 228 communicatingwith the conduit 225.

The pressure above the diaphragm 2I8 is controlled by an electric valve221 and a throttling valve 228, the two valves being in seriesin atube228 which conveys gas from the chamberabove the diaphragm to anauxiliary pilot-bumer 220. whenever both valves are open. The modulating valve 228 may be of a conventional type having a valve memberwhich is automatically I positioned byelement 250. The element 250corresponding to the element 50 of Figure 1, and the v device 248 as awhole being similar'to the de- I spaces-but will carry heat awayfrom thefurvice 48 of. Figure .1. The valve 221 and the I produce a small amountof heat adjacent the,

thermostat.

In operation the valve 210 is opened and closed in response to openingand closing of thermostat 232 and corresponding opening and' closing ofvalve 221, the valve 228 always being in a partly open position. closesindicating a need for heating a circuit is establishedfor opening valve212! a follows: from wire 25! through heater 238, thermostat. 232,.fixed contact 252,, wire 256, wire 254, valve 221' back to wire 258. Thewires 25| and 258 maybe connected to any-suitable source of power.Whenever valve 221 is opened pressure will be released from abovediaphragm H6 and will be bled oil at a rate determined by the positionof valve 228. Heater 253 of the device 248 is energized whenever thethermostat is calling for heat through the following circuit: from wire25l through heater 23B, thermostat 232, contact 252, wire 25E, wire 259,heater 253, wire 260 back to wire 258. The position of valve 228 will ofcourse be determined by the device 248 and-the position of element 250of device 248 will be determined by the relationship between theduration of on and off cycles of the thermostat as described inconnection with previous embodiments. When thermostatic cycles arelonger element 250 will position valve 228 to a wider open position soas to supply gas at a greater rate. It will be seen therefore that atincreased heating loads the heating capacity of the system will begreater and less time will be required upon each demand for heat for thesystem to bring the temperature back up to the required value.

In ordinary on and oil temperature controlled systems the capacity ofthe system is ordinarily fixed. When a heavy load is imposed on a systemthe temperature may depart appreciably from the desired value and itwill take a long period of operation for it to be brought back to thedesired value. In my system the capacity of the heating apparatus isincreased proportionately to the load so that the temperature can bemore readily efficient and quickly brought back to the desired valueafter it deviates therer from. In the system of Figure 3 as the loadincreases the capacity of the system is also increased. As the load onthe system increases the thermostatic cycles become longer but becauseof the increase in capacity of the system anticipate the arrival of heatfrom the heating source which would be sumcient to open the thermostat.

The system of Figure 4.- is: similar to that of Figure 3 except that thethermostat and the device 368 are utilized to control main valvesinstead of pilot valves. In Figure 4 valve 321 is Whenever thethermostat 232 an electric valve in a main gas line. 325 connected to a'burner 304. The valve 328 corresponds to' the throttling valve 223 andis interposed in a branch conduit 324 leading to a second burner 305.Hand valves 32B and 32l are I interposed in the conduits 301 and 324,respectively. .Whenever the thermostat 332 indicates a need for heat acircuit is completed for opening the valve 321 as follows: from wire 35lthrough heater 336, thermostat 332, contact 352, wire- 355, wire 354,valve 32?, wire 355 back to wire 358. Whenever the thermostat is callingfor heat the element 353 is also energized through the followingcircuit: from wire 35| through heater 335-, thermostat 332, contact 352,wire 356, wire 358,. heater 353, wire 368, back to wire 358. Wheneverthe thermostat 332 is calling for heat a minimum amount of gas passesthrough the valve 328 depending upon its 'adjustment and an additionalquantity of gas passes a demanded is adjusted correspondingly totheload.

The system of Figure 4 has the same advantages and novel results aspointed out in connection with Figure 3. 1

The representative embodiments of the invention which have beendisclosed are exemplary forms which it may take. The disclosedembodiments are illustrative and the invention is to be limitedonly inaccordance with the scope of the appended claims.

I claim as my invention:

1. In a temperature control system, in combination, variable capacitytemperature changing equipment, a thermostat responsive to a medium thetemperature of which is modified by said temperature changing equipment,means whereby said thermostat may cause intermittent operation of' saidequipment, means for varying the capacity of said temperature changingequipment, said last mentioned means comprising a temperature responsiveswitch means independent of the thermostat and having substantialthermal mass, means for heating said switch means, said heating meansbeing controlled in accordance with the operation and non-operation ofthe temperature changing equipment whereby the rate of heat inputto theswitch means and its resultant net temperature are determined by theratio between the time of operation and the time of non-operation of thetemequipment, a thermostat responsive to a medium operation andnon-operation of the temperature changing equipment to cause operationof the operation and the aggregate duration switch heating means duringone of said conditions of the temperature changing equipment and torendersaid heating'means inoperativeduring thevother of said conditions,whereby the rate,of heat input to the switch means and its resultantnettemperature are determined by the of said means for varying the heatexchange ca- -pacity of the heat exchange eq ipment upon closing andmeans controlled by said switch for additionally heating the switch andtending to ratio between the time of operation and the time ofnon-operation o! the temperature changing equipment, and meansresponsiveito said switch means operativeto eflect a change in-thecapacity of the temperature changing equipment when the temperatureaffecting the switch means reaches a predetermined value, and means foradjusting said heating means whereby the ratio between the time ofoperation. and non-operation of said temperature changing equipment atwhich said switch means brings about a change in the capacity of thetemperature changing equipment may be varied.

3. In a temperature control system, in combination, variablecapacitytemperature changing equipment, a thermostat responsive to a medium thetemperature of which is modified by said temperature changing equipment,means whereby said thermostat may intermittently operate said equipment,control means responsive to the relationship between the aggregateduration of of inoperation of the temperature changing equipment, saidlast mentioned means being movable independent of the thermostat andassuming a pre determined average position depending on said keep it inclosed position, and means for adjusting'the rate of heating of saidheater.

6. In a temperature control system in combi nation, heat exchangeequipment, a space thermostat for controlling said equipment to maintaina given temperature, means for varying the I ,heat exchange capacity ofthe equipment, said switch for. additionally heating the switch andtending to keep it in closed position, and variableres istance means foradjusting heating of the switch\ when the thermostat is not satisfiedwhereby the ratio of time oiheating and cooling of the switchnecessary'ior its iilosure can be adjusted.

relationship and means responsive to said control means operating tovary the capacity of the temperature changing equipment when saidrelationship between the aggregate duration of operation and thaggregate duration of inoperation of the temperature changing equipmentassumes a predetermined ratio, and means for varying the relationshipbetween aggregateduration of operation and inoperation of the temperature changing equipment at which a change 'in capacity thereof isbrought about. 4. In a temperature control system in combination, heatexchange equipment, a space thermostat for controlling said equipment tomaintain a given temperature, means for varying the 7. In a system oftemperature control, in combination, a temperature changer operable at avariable heat-exchange rate, a thermostat controlling saidtemperature"changer, means for varying the temperature changing efl'ect' oi thetemperature changer comprising aheat responsive switch independent ofthe thermostat and having substantial thermal mass, and means forheating the switch when the thermostat is not satisfied, saidswitch'icooling when the thermostat is satisfied, 'said switch assuminga net temperature depending upon the ratio of heating to cooling of theswitch as determined by the thermostat and means controlled by saidswitch opheat exchange capacity of the equipment, said means comprisinga heat actuated switch movable, independent of the thermostat, anelectric heater for the switch, said heater being controlled by thethermostat whereby the switch is heated when the thermostat is notsatisfied, said switch accumulating suflicient heat to cause closurethereof depending upon th proportionate time of heating thereof, saidswitch eflecting operation of said means for varying the heat exchangecapacity of the heat exchange equipment upon closing and meanscontrolled-by the switch for additionally heating the-switch and tendingto keep it in closed position. i r

5. In a. temperature control system in combination, heat exchangeequipment, a space thermostat for controlling said equipment to maintaina given temperature, means for varying the heat exchange capacity of theequipment, said means comprising a heat actuated switch movableindependent of the thermostat, an electric erative to varythe heatexchange rate temperature changer.

8. In a temperature control system, in combination, temperature changingequipment for changing thetemperature of a heat transporting of themedium, means for circulating heat transporting medium to a space, athermostat controlling said equipment for maintaining a giventemperature in" the space, means comprising a thermal switch independentof the thermostat, said last mentioned means including a heatercontrolled by the thermostat for heating the switch when heat is beingsupplied to the spacasaid switch cool ing when heat is not beingsupplied to thespace, the rate of heat input to the switch depending onthe ratio ot'timei it is heated to the time-ltis not heated, said switcha predetermined position depending on the rate of heatinput thereto,said switch clomng at'a predetermined rate of heat input thereto, andmeans responsive to said switch for increasing the circulation' of heattransporting medium to thespace;

9. In a temperature control system, in combination, a'temperaturechanging means, a therheater for the switch,- said heater beingcontrolled by the thermostat whereby the switch is heated when thethermostat is not satisfied, said switch accumulating sufficient-heat tocause closure thereof depending-upon the relative aggregate time ofheating and aggregate time when it is not heated, said switcheflecting-operation mostat controlling said means, a thermalswitchindependent oi the thermostat and having substantial thermal mass, meansfor supplying heat to the switch when the thermostat is indicating aneed for operatlon oi the temperature changing means, saidswitch'heating means beinginoperative and the switchdissipating heatwhen'temperature changing means, said switch means being arranged so thatdissipation of heat there- '1 from is retarded, said switch appreciablychanging its position only in response to the average rate of heat inputthereto determined by .the relative duration of time when'heat is beingsup plied thereto and when heat is not supplied thereto over asubstantial period of time, and means responsive to said switch forvarying the temperature changing effect of the temperature changingmeans.

10. In a temperature control system, in combination, a temperaturechanging means, a thermostat controlling said means, means for vary-,ing the temperature changing efiect of said temperature changing meanscomprising a thermal switch independent of the thermostat and havingsubstantial thermal mass, means for supplying heat to the switch whenthe thermostat is indicating a need for operation of thetemperaturechanging means, said switch heating means being inoperative and theswitch dissipating heat when the thermostat does not call for operationof the temperature changing means, said switch means beingarranged sothatdissipation of heat iary control device todiflerent positionsopera.- tiveimdependency-on the, duration and fre-' quencyflot theoperative and inoperative periods of said-equipment, and means forvarying the heat exchange operating rate-of said equipment operative independencyonthe position of the g r auxiliary control device.

therefrom is retarded, said switch-appreciably" changing its positiononly in response to the average rate of heat input thereto determined bythe relative duration of time when heat is being supplied thereto andwhen heat is not supplied thereto over a substantial period of time, andmeans controlled by said switch for additionally supplying heat thereto.

11. In apparatus of the characterdescribed, in combination, heatingmeans for heating a medium, thermostatic means operative to turn theheating means on at a predetermined temperature and off at anotherpredetermined temperature, said thermostatic means being respon sive tothe temperature of the medium so that the relative duration of the ofiperiods and the on periods of the heating means'depends upon the heatingrequirements, control mean responsive to the relative duration of thealternate on and oflz periods comprising a heat responsive devicecapable of movement independent of said thermostatic means, means forheating the device, means for rendering said device heating meansoperative during the periods of one of the alternating series of onperiod and off periods of the heating means, the device dissipating heatduring the periods of the, other said series, whereby the device assumesa position depending upon the rate of heat input thereto as determinedby the relative lengths of the said on period; and ofi periods of thheating means, and means responsive to the position of said controlmeans operative to adjust the rate of heating of said heat means. i

12. In a temperature regulating system, temperature changing equipmentvariably operative at different heat exchange rates for changing thetemperature of a fluid medium, a thermostat movable in response tovariations in temperature of said medium to be regulated operative toinitiate temperature changing operation of said.

13. In a temperature regulating system, tem perature changing equipmentvariablyoperative at different heat exchange rates for changing thetemperature of a fluid medium, a thermostat movable in response tovariations in temperatur of said medium to be regulated operative in anon position to initiate temperature changing operationiot said equipmentat one predetermined temperature and operative in an off position toterminate said operation of said equipment at another predeterminedtemperature, a heat responsive auxiliary control device capable ofmovement independent of the thermostat and measuring the operatingdemand on said equipment, heating means rendered operative. by thethermostat in one of its on and off positions, and rendered inoperativewhen "the I thermostat isin the other of.-said positions, for

intermittently heating and adjusting the auxiliary control device todifierent positions in accordance with the relative duration of thealternate operative and inoperative periods of the equipment, and meansfor varying the heat exchange operating rate of the equipment operativein dependency on the position of the auxiliary control device.

14. In a temperature regulating system, temperature changing equipmentvvariably operative at different heat exchange rates, for changing thetemperature of a fluid medium, a thermostat movable in response tovariations in temperature of said medium to be regulated operative toinitiate .temperature changing operation of said equipment at onepredetermined temperature and terminate said operation of said equipmentat another predetermined temperature, auxiliary control mechanismmeasuring the operating demand on the equipment including a heatresponsive member free of direct connection with the thermostat adaptedto move in one direction along a path upon heating and to move in theopposite direction along its path upon cooling, means operating to heatthe member during each operating period of the equipment to advance.

the member along its path in one direction to an extent dependent on thduration ofsuch periods, and means for rendering said heating meansinoperative during each inoperative-period of the equipment and causingthe member to cool and advance along its path in the opposite directionto an extent dependent on the duration of such latter periods, and meansfor varying the heat exchange operating rate of the equipment operativein dependency on the position of said movable member of the auxiliarycontrol mechanism. I

15. In a temperature regulating system, an intermittently operativetemperature changing equipment comprising a first unit and a second unitfor changing the temperature of a fluid equipment at one predeterminedtemperature to the thermostat, means for adjusting the auxilmedium at aplurality of heat exchange rates, a thermostat movable in response tovariations in temperature of said medium to be regulated operative toinitiate temperature changing operation of one of said units at apredetermined temperature and terminate said operation of said unit atanother predetermined temperature, an auxiliary control device capableof movement independentof the thermostat and measuring the operatingdemand on the equipment at the heat exchange rate produced by said oneunit, means for adjusting the auxiliary control device to diftive toinitiate operation of the equipment at one predetermined temperature andterminate said.

operation of said equipmentat'another predetermined temperature,-therelative duration of '-the of! and on periods of the thermostat and thetemperature changing equipment depending on the demand upon theequipment, a heat responsive control device capable of movementindependent of the thermostat and measuring the operating demand on theequipment, heating means rendered'operative by the thermostat in-perature of said medium to'be regulated operaone of its on and of!positions, and rendered inoperative when the thermostat is in the otherof said positions, for intermittently heating said heat responsivedevice and effective to produce gradual movement thereof to differentpositions in accordance with the relative duration ofthe alternateoperative and inoperative periods oi the equipment and meansiorgradually varying the heat exchange operating rate of the equipmentoperative in dependency on the position of the heat responsive controldevice.

WILLIAM L McGRATH.

